Turbocharger diffuser center body

ABSTRACT

A turbocharger turbine having housing walls defining a diffuser. Within the diffuser, a center body within the diffuser is supported by de-swirl vanes extending from the diffuser wall. The center body forms a de-swirl passageway having an increasing mean diameter of flow from an upstream end of the center body to a leading edge of the de-swirl vanes. A trailing edge of the de-swirl vanes is near the downstream end of the center body. Annular-type guide vanes surround the center body within the de-swirl passageway. A wastegate system is configured to vent wastegate flow into the diffuser through injection ports on the de-swirl vanes, annular guide vanes and/or center body.

The present invention relates generally to turbocharger turbines, andmore particularly, to an exhaust gas diffuser configuration for a radialautomotive turbocharger turbine.

BACKGROUND OF THE INVENTION

Radial turbocharger turbines are provided with diffusers extendingaxially downstream from a turbine wheel around a wheel centerline. Thediffuser is configured to reduce airflow velocity. To accomplish this,the cross-sectional area of the diffuser increases from an upstream endof the diffuser to the downstream end of the diffuser. Because the massflow rate through the diffuser is constant, this increasedcross-sectional area provides for decreased velocity, decreased dynamicpressure, and increased static pressure.

Turbines are designed for optimal operation at a design operatingcondition. At this operating condition, an exhaust gas stream will enterthe diffuser having substantially axial flow. Nevertheless, at so called‘off design’ operating conditions (i.e., substantially differentoperating conditions than the design operating condition), the exhaustgas stream may be characterized by high exit swirl, which can be ineither direction depending on the particular operating condition. Theseoff design operating conditions occur frequently in turbocharger turbineoperation due to pulsing inlet flow conditions, size constraints (e.g.,a turbine diameter smaller than optimum), and conditions where variablenozzle guide vanes (in the turbine inlet) are operated away from theirnominal position. These off design operating conditions result in a verylow blade speed ratio condition for the turbine stage which results in ahigh degree of exit swirl.

Thus, in these off design operating conditions, while the downstream(i.e., axial portion of the) velocity of the exhaust gas stream passingthrough the diffuser is reduced, it will still have a significanttangential (i.e., circumferential) velocity portion (i.e., a circularmotion around the axial direction). This tangential velocity portion, incombination with the axial velocity portion, creates a swirling (i.e.,spiraling) exhaust gas stream. This tangential velocity portionincreases the total kinetic energy of the exhaust stream over that ofjust the axial velocity portion, and thereby causes efficiency lossesacross the off design operating range of the turbine, particularly undertransient conditions.

It should be noted that any effort to deal with this problem isconstrained by size limitations for the turbocharger, i.e., packageconstraints. This is particularly true for automotive turbochargers,which typically have significant size limitations.

A traditional conical diffuser design can be very efficient when dealingwith zero or low levels of inlet swirl. Nevertheless, applying atraditional conical diffuser design to a swirling flow with packageconstraints typically results in significant separation of the flow andinefficient diffusion. De-swirl vanes with their leading edge anglematched to the flow swirl angle can be used in attempt to manage theproblem, but these only operate effectively at a small range ofoperating conditions because the swirl angle of the flow into thediffuser varies dramatically across the useful operating range of theturbine. Thus, the use of de-swirl vanes results in high (angle of)incidence losses into the de-swirl vanes at operating conditions thatare not close to the operating conditions for which the vanes weredesigned.

Accordingly, there has existed a need for an automotive turbochargerturbine diffuser that is both compact and highly efficient in reducingthe kinetic energy of an exhaust gas stream.

SUMMARY OF THE INVENTION

In various embodiments, the present invention may solve some or all ofthe needs mentioned above, providing a compact automotive turbochargerturbine diffuser that is highly efficient in reducing the kinetic energyof an exhaust gas stream.

The turbocharger turbine includes a turbine wheel and a turbine housing.The housing has housing walls that define a turbine passageway extendingaxially. The passageway includes a wheel chamber containing the turbinewheel. The wheel chamber extends downstream from an inducer to anexducer of the turbine wheel. The passageway further includes an outletpassage extending downstream from the exducer. This outlet passagedefines a diffuser having a diffuser wall that increases in axiallycross-sectional size from an upstream end of the diffuser to adownstream end of the diffuser.

The turbocharger turbine features a center body within the diffuser.This center body has a center body wall forming a de-swirl passagewaywithin the diffuser wall and surrounding the center body.Advantageously, the presence of the center body increases the meandiameter of the exhaust gas stream. With free vortex flow, the angularmomentum of the tangential portion of the flow remains constant, andthus the increase in mean diameter decreases the tangential velocity ofthe exhaust stream.

The turbine further features one or more de-swirl vanes that support thecenter body. These de-swirl vanes extend between the center body walland the diffuser wall. Additionally, the turbine further features thatthe de-swirl passageway is characterized by an increasing mean diameterof flow from an upstream end of the center body to a leading edge of theone or more de-swirl vanes. Advantageously, the decreased tangentialvelocity of the exhaust stream reduces the angle of attack with whichthe exhaust gas stream strikes the de-swirl vanes during non-standardoperating conditions. This decrease in the angle of attack reduces angleof incidence losses over a wide range of operating conditions. Thisreduces efficiency losses across the off design operating range of theturbine, particularly under transient conditions.

The turbine also features that a trailing edge of the de-swirl vanes islocated in the close axial vicinity of the downstream end of the centerbody. Advantageously, the de-swirl vanes prevent free vortex flow, sothe angular momentum of the tangential portion of the flow does notremains constant. As a result, the cross-sectional area of the streamcan be significantly increased and the mean diameter can be decreasedwithout increasing the tangential velocity of the exhaust stream.

The turbine also features annular-type guide vanes surrounding thecenter body between center body wall and diffuser wall. Advantageously,the annular-type guide vanes prevent separation of flow in the de-swirlpassageway.

Finally, the turbine features a wastegate system that injects wastegateflow into the flow from the turbine exducer via injection ports formedin the center body, de-swirl vanes and/or annular guide vanes.Advantageously, this might be found to improve the diffusing flow in therear section of the diffuser.

Other features and advantages of the invention will become apparent fromthe following detailed description of the preferred embodiments, takenwith the accompanying drawings, which illustrate, by way of example, theprinciples of the invention. The detailed description of particularpreferred embodiments, as set out below to enable one to build and usean embodiment of the invention, are not intended to limit the enumeratedclaims, but rather, they are intended to serve as particular examples ofthe claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system layout of an internal combustion engine with aturbocharger and a charge air cooler embodying the present invention.

FIG. 2 is a cut-away perspective view of a turbine housing of theturbocharger of FIG. 1, and a related center body with vanes.

FIG. 3 is a second cut-away perspective view of a turbine housing of theturbocharger of FIG. 1, and a related center body with vanes.

FIG. 4 is a cut-away front schematic view of the turbine housing of FIG.2, showing a center body and vanes.

FIG. 5 is a cut-away front perspective view of a turbine housing of asecond embodiment of the invention, showing wastegate injectionfeatures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention summarized above and defined by the enumerated claims maybe better understood by referring to the following detailed description,which should be read with the accompanying drawings. This detaileddescription of particular preferred embodiments of the invention, setout below to enable one to build and use particular implementations ofthe invention, is not intended to limit the enumerated claims, butrather, it is intended to provide particular examples of them.

Typical embodiments of the present invention utilize an increase in themean diameter of an exhaust gas stream (i.e., of flow) directly afterthe turbine wheel exit to reduce the swirl angle of the flow. Thisprovides for axial or close-to-axial de-swirl vanes to be used throughthe remainder of the diffuser without significant angle of incidencelosses over a wide range of operating conditions. In this way, effectivediffusion can be managed over a wide range of inlet swirl angles, andtherefore a wide range of the turbine operating conditions.

With reference to FIG. 1, in a first embodiment of the invention, aturbocharger 101 includes a turbocharger housing and a rotor configuredto rotate within the turbocharger housing along an axis of rotorrotation 103 on thrust bearings and journal bearings (or alternatively,other bearings such as ball bearings). The turbocharger housing includesa turbine housing 105, a compressor housing 107, and a bearing housing109 (i.e., center housing) that connects the turbine housing to thecompressor housing. The rotor includes a turbine wheel 111 locatedsubstantially within the turbine housing, a compressor wheel 113 locatedsubstantially within the compressor housing, and a shaft 115 extendingalong the axis of rotor rotation, through the bearing housing, toconnect the turbine wheel to the compressor wheel.

The turbine housing 105 and turbine wheel 111 form a turbine configuredto circumferentially receive a high-pressure and high-temperatureexhaust gas stream 121 from an engine, e.g., from an exhaust manifold123 of an internal combustion engine 125. The turbine wheel (and thusthe rotor) is driven in rotation around the axis of rotor rotation 103by the high-pressure and high-temperature exhaust gas stream, whichbecomes a lower-pressure and lower-temperature exhaust gas stream 127that is passed through a diffuser (not shown), and then axially releasedinto an exhaust system (not shown).

The compressor housing 107 and compressor wheel 113 form a compressorstage. The compressor wheel, being driven in rotation by the exhaust-gasdriven turbine wheel 111, is configured to compress axially receivedinput air (e.g., ambient air 131, or already-pressurized air from aprevious-stage in a multi-stage compressor) into a pressurized airstream 133 that is ejected circumferentially from the compressor. Due tothe compression process, the pressurized air stream is characterized byan increased temperature, over that of the input air.

Optionally, the pressurized air stream may be channeled through aconvectively cooled charge air cooler 135 configured to dissipate heatfrom the pressurized air stream, increasing its density. The resultingcooled and pressurized output air stream 137 is channeled into an intakemanifold 139 on the internal combustion engine, or alternatively, into asubsequent-stage, in-series compressor. The operation of the system iscontrolled by an ECU 151 (electronic control unit) that connects to theremainder of the system via communication connections 153.

With reference to FIGS. 1 to 4, the turbine housing 105 has a housingwall 201 that defines a turbine passageway. This passageway includes awheel chamber 203 containing the turbine wheel 111, a radial or mixedflow turbine inlet passage (not shown) leading to an inducer (not shown)of the turbine wheel (i.e., at the leading edges of the wheel blades),and an outlet passage 205 extending downstream from an exducer 207 ofthe turbine wheel (i.e., at the trailing edge of the wheel blades). Thewheel chamber extends downstream from the inducer to the exducer of theturbine wheel.

The outlet passage 205 defines a diffuser, and the portion of thehousing wall 201 within the diffuser forms a diffuser wall 211. In thisembodiment, the diffuser wall starts at a diameter close to that of thewheel chamber 203 at the exducer 207, and then increases smoothly indiameter for a transitional (axial) distance 213 downstream of theexducer to reach a maximum diffuser wall diameter at a maximum diffuserwall diameter axial location 215. This maximum diffuser wall diameteraxial location is to be understood as the axially upstream end of thediffuser wall at that diameter.

After the transitional distance 213, the diffuser wall 211 establishes aconstant diameter in the amount of the maximum diffuser wall diameter.Thus, the diffuser wall increases in axially cross-sectional size (e.g.,diameter) from an upstream end of the diffuser to the maximum diffuserwall diameter axial location 215, and therefore to a downstream end ofthe diffuser. For the purposes of this application, it should beunderstood that a “smoothly varying surface” is one having a slope anglefunction that is continuous.

Center Body

Within the outlet passage 205 (and the diffuser) is a center body 221defining an (outer) center body wall 223. In this embodiment, the centerbody is an aerodynamic, completely rotationally symmetric body (aroundthe axis of rotor rotation 103). For the purposes of this application,complete rotational symmetry is defined to mean that the cross-sectionof the center body around the axis of rotor rotation is circular atevery axial location.

At an upstream end, the center body forms a nose 225 that is shaped as aconical cylinder having a diameter that increases in the downstreamdirection. The upstream end of this nose is substantially the size andshape of a downstream end 227 of a hub 229 of the turbine wheel 111(i.e., the nose's size and shape are close enough to accommodate theflow without causing significant disturbance in the flow). The centerbody upstream end concentrically and opposingly faces the wheel hubdownstream end, thus providing for smooth exhaust flow between the wheelexducer and the center body.

From the center body upstream end, the center body wall 223 smoothlyincreases in diameter in an axially downstream direction until itreaches a maximum diameter at a maximum center body diameter axiallocation 231. This location is in the close axial vicinity of themaximum diffuser wall diameter axial location. For the purposes of thisapplication, the phrase close axial vicinity should be understood tomean in a within a range of locations through which the velocity(direction and speed) of the flow is substantially unchanged (e.g.,changed less than five percent). Downstream of the maximum center bodydiameter axial location, the center body wall reduces smoothly indiameter down to a distal tip 233 at a downstream end of the center body221, where it may have a rounded or pointed configuration.

Vanes

The center body 221 is structurally supported within the diffuser wall211 by one or more, and more preferably by a plurality of (e.g., four)de-swirl vanes 241 extending through the de-swirl passageway between thecenter body wall 223 and the surrounding diffuser wall 211. With respectto a view in the axial direction (along the axis of rotor rotation 103),these de-swirl vanes may extend from an inner end to an outer end in apurely radial direction, or at an angle to the purely radial direction.With respect to a view in a radial direction, all of, or at least aforward portion of these vanes may extend from a leading edge 243 to atrailing edge 245 in a purely axial direction, or at an angle to theaxial direction.

While the presently depicted vanes extend from a leading edge 243 to atrailing edge 245 in a purely axial direction, there may be embodimentsin which having a non-axial tilt may be desirable. For example, in someembodiments slightly angling the vanes may effectively tune the systemto a specific target operating condition. In other embodiments, it maybe that a specific turbine stage (wheel) biases the outlet swirl in onedirection more than the other. This could be for numerous reasons, suchas turbine designs having blade angles that are not optimal formechanical design reasons.

The leading edge 243 (at an upstream end) of each de-swirl vane is inthe close axial vicinity of the maximum diffuser wall diameter axiallocation 215, and is also in the close axial vicinity of the maximumcenter body diameter axial location 231. To accommodate variation in theangle of attack of the exhaust air on the de-swirl vanes, largerdiameter leading edges are generally to be used. The trailing edge 245(at a downstream end) of each de-swirl vane extends to an upstream endof the distal tip 233. Therefore, the distal tip is the portion of thecenter body downstream of the de-swirl blade trailing edges.

Optionally, the de-swirl vanes 241 may also support annular guide vanes251 extending around (surrounding) the center body 221 between thecenter body wall 223 and the diffuser wall 211 within the de-swirlpassageway. The annular guide vanes combine to form an annulus having alarger diameter at a leading edge 253 (at an upstream end), and asmaller diameter at a trailing edge 255 (at a downstream end). Axially,the annular guide vane leading edges are slightly downstream of themaximum center body diameter axial location 231, the maximum diffuserwall diameter axial location 215, and the de-swirl vane leading edges243. In at least some embodiments, the annular guide vane leading edgesare located in the close axial vicinity of the de-swirl vane leadingedges. Axially, the annular guide vane trailing edges extend to thede-swirl vane trailing edges, and/or are located in the close axialvicinity of the de-swirl vane trailing edges.

The axial extent of center body wall 223 and the surrounding diffuserwall 211 of the outlet passage axially define an annular de-swirlpassageway within the diffuser. The de-swirl passageway is within thediffuser wall and surrounds the center body 221. From (immediatelydownstream of) the upstream end of the center body to the de-swirl vaneleading edges 243, the de-swirl passageway both increases in meandiameter, and may somewhat increase in cross-sectional area. Forconvenience, this portion of the de-swirl passageway will be defined asthe forward de-swirl passageway.

Functionality

In many typical embodiments, the forward de-swirl passageway ischaracterized by a mean diameter at the leading edges of the one or morede-swirl vanes that is in a range of 1.1 to 3.0 times the mean diameterimmediately downstream of the upstream end of the center body 221 (i.e.,where it is at approximately the same diameter as the downstream end 227of the turbine wheel hub). Likewise, in many typical embodiments, theforward de-swirl passageway is characterized by a cross-sectional areaat the leading edges of the one or more de-swirl vanes that is in arange of 0.8 to 1.5 times the cross-sectional area immediatelydownstream of the upstream end of the center body, i.e., it may be arelatively small increase to a very small decrease.

As a swirling exhaust gas stream passes out from the turbine exducer 207and then into the forward de-swirl passageway, the exhaust gas stream isdiverted radially outward by the center body wall to a larger meandiameter. The small, limited increase in cross-sectional area providesfor some decrease in axial velocity, and thereby provides decreaseddynamic pressure and increased static pressure. With free vortex flow,the angular momentum of the tangential portion of the flow remainsconstant, and thus the increase in mean diameter decreases thetangential velocity of the exhaust stream.

As a result, the swirl angle of attack of the exhaust gas stream on thede-swirl vanes 241 is significantly reduced at the de-swirl vane leadingedges 243 (as compared to de-swirl vanes used without the center body).The use of de-swirl vanes with the center body therefore is subject tolower (angle of) incidence losses into the de-swirl vanes (as comparedto de-swirl vanes used without the center body) at operating conditionsthat are not close to the operating conditions for which the de-swirlvanes were designed.

From the de-swirl vane leading edges 243 to the de-swirl vane trailingedges 245, the de-swirl passageway both decreases in mean diameter, andsubstantially increases in cross-sectional area. For convenience, thisportion of the de-swirl passageway will be defined as the aft de-swirlpassageway. The aft de-swirl passageway is subdivided into a pluralityof (e.g., four, as depicted) aft de-swirl passageway portions by thede-swirl vanes 241.

As the exhaust gas stream passes through the aft de-swirl passageway,the exhaust gas stream expands radially inward toward the recedingcenter body wall 223, thereby being characterized by a smaller meandiameter. The de-swirl vanes 241 prevent free vortex flow, and thusblock increased tangential velocity of the exhaust gas stream despitethe reduced mean diameter of that stream. At the same time, the greatlyincreased cross-sectional area provides for a significant decrease inaxial velocity, and thereby provides significantly decreased dynamicpressure and increased static pressure.

Across the distal tip 233, i.e., from the de-swirl vane trailing edges245 to the downstream end of the center body 221 (typically a very shortdistance), the de-swirl passageway slightly decreases in mean diameterand slightly increases in cross-sectional area. For convenience, thisportion of the de-swirl passageway will be defined as the firsttransitional de-swirl passageway. These changes minimally increase swirland minimally decrease axial velocity. More significantly, the firsttransitional passageway provides for a smooth aerodynamic end to thede-swirl passageway, limiting inefficient turbulence. This wholede-swirl system advantageously can occur within significant packageconstraints of a turbocharger.

If the optional annular guide vanes 251 extending around the center body221 between the center body wall 223 and the diffuser wall 211 areincluded, then each aft de-swirl passageway portion may be furtherdivided into a second transitional de-swirl passageway portion from thede-swirl vane leading edges 243 to the annular guide vane leading edges253, an inner aft de-swirl passageway portion within the annular guidevanes (i.e., between the annular guide vanes and the center body wall)from the annular guide vane leading edges to the annular guide vanetrailing edges 255, and an outer aft de-swirl passageway portion outsideof the annular guide vanes (i.e., between the annular guide vanes andthe diffuser wall) from the annular guide vane leading edges to theannular guide vane trailing edges.

The inner aft de-swirl passageway portions combine to form an inner aftde-swirl passageway. Likewise, the outer aft de-swirl passagewayportions combine to form an outer aft de-swirl passageway. The secondtransitional passageway helps prevent interference in the flow betweenthe effects of the flow by the de-swirl vane leading edges 243 and theeffects of the flow by the annular guide vane leading edges 253. Theprimary function of the annular guide vanes is to prevent separation offlow in the aft de-swirl passageway.

In an alternative embodiment where the de-swirl vane trailing edges 245extend further downstream that the annular guide vane trailing edges255, the aft de-swirl passageway further includes a third transitionalpassageway having a plurality (e.g., four) of circumferential portionsfrom the de-swirl vane trailing edges 245 to the annular guide vanetrailing edges 255. In another alternative embodiment where the de-swirlvane trailing edges 245 end upstream of the annular guide vane trailingedges 255, the first transitional passageway is subdivided into aplurality of portions.

Wastegate with Injected Flow

With reference to FIGS. 3 and 5, a second embodiment of the turbine isprovided with a wastegate system. The second embodiment is very similarto the first embodiment other than the wastegate features. The wastegatesystem provides a turbine bypass using a controllable valve 401 (as isknown), such that exhaust flow can be directly vented from a turbineinlet passage location upstream of the inducer of the turbine wheel to alocation in the outlet passageway downstream of the exducer of theturbine wheel. Rather than directly dumping the full wastegate flow intothe flow from the turbine wheel exducer (“the exducer flow”) through anopening in the outlet passageway wall, the present embodiment injectswastegate flow into the outlet passageway from within the exducer flow.

The wastegate system forms passageways, being serially defined by thewastegate controllable valve 401, a flow channel 403, a wastegateexhaust port 405 in the outlet passageway wall, and an injection body.The wastegate system controllably places the outlet passage in fluidcommunication with an exhaust flow upstream of the inducer (i.e., aninlet flow). The injection body has interior walls that define a hollowinterior of the injection body, the hollow interior being in directfluid communication with the wastegate exhaust port (i.e., it directlyconnects wastegate flow from the wastegate exhaust port without thewastegate flow first intermixing with the exducer flow). The injectionbody in turn injects the wastegate flow into the exducer flow fromwithin that exducer flow through one or more injection ports 409.

The injection body includes one or more injection body supports 411 thatconnect to the outlet passageway wall downstream of the exducer. Theinjection body supports form a hollow interior that is in direct fluidcommunication with the wastegate exhaust ports 405.

Optionally, the injection body may also include an injection center body413 within the walls of the exducer flow (i.e., inside the wall of theoutlet passageway). The injection center body may form a hollow interiorthat is in direct fluid communication with the hollow interior of theone or more injection body supports. The injection center body isstructurally supported within the wall of the outlet passageway by theinjection body supports. The injection ports 409 place the hollowinterior of the injection body in fluid communication with the exducerflow from within the exducer flow (i.e., within and at a distance fromthe outlet passageway wall).

Optionally, the injection body may include other structures. Forexample, may include hollow injection annular vanes 415. These injectionannular vanes might or might not form injection ports 409.

In the present embodiment, the injection body includes the previouslydescribed de-swirl vanes 241, annular guide vanes 251 and center body221. The four de-swirl vanes 241 are the one or more injection bodysupports 411 that connect to the outlet passageway wall downstream ofthe exducer. The center body 221 is the injection center body 413, andthe annular guide vanes 251 are the injection annular vanes 415. Some orall of the de-swirl vanes are hollow. Optionally, the annular guidevanes and/or the center body are also hollow, placing the four de-swirlvanes in fluid communication with one-another. At the outlet passagewall, the de-swirl vanes connect to flow wastegate exhaust ports 405that place the wastegate flow from the controllable wastegate valve influid communication with the hollow interiors of the de-swirl vanes.

The injection ports 409 could be formed in any or all of the de-swirlvanes, the annular guide vanes and the center body. For example, withthe de-swirl vanes and the center body hollow, the injection ports mightbe formed in only the center body. The wastegate flow could then exitthrough the rear side of the centre body through one or more injectionports to mix with the exducer flow. This might be found to improve thediffusing flow in the rear section of the diffuser.

OTHER EMBODIMENTS

While the present embodiment is characterized by a circular duct and acenter body having circular cross-sections (when taken perpendicular tothe axial direction), embodiments having other axial cross-sectionalshapes are contemplated within the scope of the invention. There can bevarious reasons for non-circular embodiments, such as packageconstraints. These non-circular embodiments may be considered to haveannular-type passageways and annular-type guide vanes, in that they area non-circular variation of their annular counterparts. For the purposeof this application, the term annular-type should be understood toinclude ring-like passageways and structures, including both onescharacterized by circular and non-circular cross-sections, that arefurther characterized by inner and outer boundaries surrounding an axis.

Other embodiments of the invention may employ variations of theabove-described elements. For example, while the diffuser wall isdescribed as increasing in size to a maximum diffuser wall diameteraxial location, alternative embodiments could employ a diffuser wallthat increases significantly prior to reaching the de-swirl vanes, andthen continues to increase in size for some distance after the de-swirlvanes. Thus, the detailed description of particular preferredembodiments, as set out above to enable one to build and use anembodiment of the invention, are not intended to limit the enumeratedclaims, but rather, they are intended to serve as particular examples ofthe claimed invention.

The present invention may be incorporated into a wide variety ofturbocharger turbines. For example, it may be used with both fixedgeometry and variable geometry turbines.

It is to be understood that various embodiments of the inventioncomprise apparatus and related methods for turbine efficiency.Additionally, the various embodiments of the invention can incorporatevarious combinations of the features described above with other relatedefficiency features. In short, the above disclosed features can becombined in a wide variety of configurations within the anticipatedscope of the invention.

What is claimed is:
 1. A turbocharger turbine, comprising: a turbinewheel; a housing having housing walls that define a turbine passageway,the passageway including a wheel chamber containing the turbine wheel,the wheel chamber extending downstream from an inducer to an exducer ofthe turbine wheel, and an outlet passage extending axially downstreamfrom the exducer, wherein the outlet passage defines a diffuser having adiffuser wall that increases in axially cross-sectional size from anupstream end of the diffuser to a downstream end of the diffuser; and acenter body within the diffuser, the center body having a center bodywall forming a de-swirl passageway within the diffuser wall and formingthe periphery of the center body; characterized in that the center bodyis supported within the diffuser by one or more de-swirl vanes extendingbetween the center body wall and the diffuser wall; an upstream end ofthe center body is substantially the size of a downstream end of a hubof the turbine wheel; the de-swirl passageway has by an increasing meandiameter of flow from the upstream end of the center body to a leadingedge of the one or more de-swirl vanes; the leading edges of thede-swirl vanes are located in the close axial vicinity of a maximumdiffuser wall diameter axial location; the leading edges of the de-swirlvanes are in the close axial vicinity of the maximum center bodydiameter axial location; and downstream of the maximum center bodydiameter axial location, the center body wall reduces smoothly indiameter down to a distal tip at a downstream end of the center body. 2.The turbocharger turbine of claim 1, wherein the de-swirl passageway ischaracterized by a mean diameter at the leading edge of the one or morede-swirl vanes that is in a range of 1.1 to 3.0 times a mean diameterimmediately downstream of an upstream end of the center body.
 3. Theturbocharger turbine of claim 2, wherein the de-swirl passageway ischaracterized by a cross-sectional area at the leading edge of the oneor more de-swirl vanes that is less than 1.5 times a cross-sectionalarea immediately downstream of an upstream end of the center body. 4.The turbocharger turbine of claim 1, wherein from a leading edge to atrailing edge, the de-swirl vanes extend axially in a purely axialdirection.
 5. The turbocharger turbine of claim 1, wherein from an innerend to an outer end, the de-swirl vanes extend radially in a purelyradial direction.
 6. The turbocharger turbine of claim 1, wherein atrailing edge of the de-swirl vanes is located in the close axialvicinity of the downstream end of the center body.
 7. The turbochargerturbine of claim 1, and further including annular-type guide vanessurrounding the center body between center body wall and diffuser wall.8. The turbocharger turbine of claim 7, wherein a leading edge of theannular-type guide vanes is located downstream of a leading edge of thede-swirl vanes.
 9. The turbocharger turbine of claim 7, wherein aleading edge of the annular-type guide vanes is located in the closeaxial vicinity of a leading edge of the de-swirl vanes.
 10. Theturbocharger turbine of claim 9, wherein a trailing edge of theannular-type guide vanes is located in the close axial vicinity of atrailing edge of the de-swirl vanes.
 11. The turbocharger turbine ofclaim 7, wherein a trailing edge of the annular-type guide vanes islocated in the close axial vicinity of a trailing edge of the de-swirlvanes.
 12. A method of de-swirling an exhaust gas stream in aturbocharger turbine, wherein the turbine includes a turbine wheel, anda housing having housing walls that define a turbine passagewayextending axially, the passageway including a wheel chamber containingthe turbine wheel, the wheel chamber extending downstream from aninducer to an exducer of the turbine wheel, and an outlet passageextending downstream from the exducer, wherein the outlet passagedefines a diffuser having a diffuser wall that increases in axiallycross-sectional size from an upstream end of the diffuser to adownstream end of the diffuser, comprising: expanding the portion of theexhaust stream coming from the exducer to a larger mean diameter arounda center body within the diffuser, the center body having a center bodywall forming a forward de-swirl passageway and an aft de-swirlpassageway within the diffuser wall and surrounding the center body,wherein expansion of the exhaust gas stream occurs in the forwardde-swirl passageway; passing the expanded exhaust gas stream through theaft de-swirl passageway such that the exhaust gas stream strikes one ormore de-swirl vanes; and contracting the exhaust gas stream that hasstruck the one or more de-swirl vanes in the aft de-swirl passageway,wherein the center body wall reduces smoothly in diameter down to adistal tip at a downstream end of the center body.
 13. The method ofclaim 12, wherein the de-swirl passageway is characterized by a meandiameter at the leading edge of the one or more de-swirl vanes that isin a range of 1.1 to 3.0 times a mean diameter immediately downstream ofan upstream end of the center body.
 14. The method of claim 12, furthercomprising dividing the exhaust gas stream between an aft inner de-swirlpassageway and an aft outer de-swirl passageway, the aft inner de-swirlpassageway and aft outer de-swirl passageway portion being separated byone or more annular-type guide vanes surrounding the center body betweencenter body wall and diffuser wall.